1. Field of the Invention
This invention relates to a video signal processing apparatus arranged to digitally perform a signal processing action on a video signal.
2. Description of the Related Art
Video cameras have rapidly become popular as a result of a reduction in size and an increase in recording density and are examples of video signal processing apparatuses:
As a result of the progress of semiconductor technology, it has recently been proposed to replace an analog signal processing action conventionally carried out within a video camera with a digital signal processing action by using an analog-to-digital (hereinafter referred to as A/D) converter and a digital-to-analog (hereinafter referred to as D/A) converter which operate at high speeds for processing a video signal within the video camera.
The video camera of the kind performing digital signal processing is described below with reference to FIG. 1, which is a block diagram showing the video camera:
A shooting or image pickup action is first described. An object image formed by a lens which is not shown is photo-electrically converted by a CCD (image sensor) 51. After that, the electrical signal thus obtained is supplied through a correlated double sampling (hereinafter referred to as CDS) circuit 52 and an automatic gain control (hereinafter referred to as AGC) circuit 53 to an A/D converter 54. The A/D converter 54 converts this signal from an analog signal into a digital signal.
The digital signal is sent to one-horizontal period delay (hereinafter referred to as 1HDL) circuits 55 and 56. Delayed signals which are thus obtained by the 1HDL circuits 55 and 56 are respectively inputted to a camera luminance (Y-) processing circuit 57 and a camera chrominance (C-) processing circuit 58. The camera Y-processing circuit 57 forms a luminance signal (hereinafter referred to as Y signal) from the digital-converted image pickup signal. The Y signal is supplied to an adder 59 to have a synchronizing (hereinafter referred to as sync) signal added thereto and is then inputted from the adder 59 to a recording/reproducing Y-processing circuit 68.
The recording/reproducing Y-processing circuit 68 performs processes such as an emphasis process, etc., necessary for magnetic recording. The digital signal which is thus processed is supplied to a D/A converter 69 to be converted into an analog signal. The analog signal is supplied to a modulator-demodulator 70 to be frequency-modulated there.
Meanwhile, the camera C-processing circuit 58 forms two color-difference signals including R-Y and B-Y signals from the digital-converted image pickup signal. The two color-difference signals are modulated into a chrominance signal (hereinafter referred to as C signal). The C signal is sent to a recording/reproducing C-processing circuit 71. At the recording/reproducing C-processing circuit 71, the frequency of the C signal is down-converted. The down-converted C signal is then supplied to a D/A converter 72 to be converted into an analog C signal.
The luminance signal (Y signal) which has been frequency-modulated and the chrominance signal (C signal) which has been frequency-down-converted are combined with each other at an adder 73 and then recorded on a video tape 86 through a recording amplifier 74, a change-over switch 75 and a recording/reproducing head 76.
In a case where an external input video signal is to be recorded and the video signal is inputted in a state of being separated into a luminance (Y) signal and a chrominance (C) signal, a recording action is performed as follows: the luminance signal included in the input signal from an external equipment which is not shown is converted into a digital signal by an A/D converter 60. The digital luminance signal thus obtained is inputted to the recording/reproducing Y-processing circuit 68 via a change-over switch 66. Signal processing actions to be carried out after the recording/reproducing Y-processing circuit 68 are similar to the processes performed in recording the image pickup signal as described above.
Meanwhile, the chrominance signal included in the external input video signal is converted by an A/D converter 62 also into a digital signal. This digital signal is inputted to the recording/reproducing C-processing circuit 71 via a change-over switch 67. The signal processing actions after the recording/reproducing C-processing circuit 71 are similar to the above-stated processes performed in recording the image pickup signal.
In recording an external input video signal, if the input video signal is a composite video signal, the recording action is performed as described below:
The input composite video signal from external equipment which is not shown is converted into a digital signal by an A/D converter 61. The digital signal thus obtained is inputted to a Y/C separation circuit which is composed of a 1HDL 63, an adder 64 and a subtracter 65 to be separated into Y (luminance) and C (chrominance) signals. After that, the Y signal is inputted to the recording/reproducing Y-processing circuit 68 via the change-over switch 66. Meanwhile, the C signal is inputted to the recording/reproducing C-processing circuit 71 via the change-over switch 67.
The processes to be carried out after the recording/reproducing Y-processing and C-processing circuits 68 and 71 are similar to the processes performed in processing the image pickup signal as described in the foregoing.
Next, signal processing to be performed at the time of reproduction is as described below:
The signal recorded on the video tape 86 is read out by the recording/reproducing head 76. The output of the recording/reproducing head 76 is amplified to a given level by a head amplifier 77 through the change-over switch 75. The reproduced signal which is thus amplified is inputted to a high-pass filter (hereinafter referred to as HPF) 78 and to a band-pass filter (hereinafter referred to as BPF) 80. A frequency-modulated luminance signal is separated from the reproduced signal by the HPF 78. The separated luminance signal is demodulated by a demodulator 70 and is then converted into a digital signal by an A/D converter 79. The digital Y signal thus obtained is inputted to the recording/reproducing Y-processing circuit 68 to be subjected to processes which are carried out reversely to the processes performed for recording.
A down-converted chrominance signal is separated from the reproduced signal by the BPF 80. The chrominance signal thus obtained is converted into a digital signal by an A/D converter 81. The digital chrominance signal is inputted to the recording/reproducing C-processing circuit 71 to be subjected to processes which are carried out reversely to the processes performed for recording.
The Y and C signals which are thus converted into their original signals are respectively converted into analog signals by D/A converters 82 and 83 in their separated states. The analog Y and C signals are then outputted either as they are, as line outputs, or in the form of a composite video signal after the Y and C signals are combined with each other by an adder 84.
Further, the luminance signal (Y signal) which has been converted by the D/A converter 82 into an analog signal is supplied also to an electronic viewfinder (hereinafter referred to as EVF) 85 for monitoring.
Further signal processing actions on the video signal are performed by various processing circuits for a higher picture quality and a higher resolution in addition to the basic signal processing actions described above.
For example, the recording/reproducing Y-processing circuit 68 and/or the recording/reproducing C-processing circuit 71 is arranged to include a 1HDL circuit. At the time of reproduction, the 1HDL circuit is used for a process of removing a crosstalk component, a process of emphasizing vertical edge parts (hereinafter referred to as vertical enhancing), a process of preventing any sudden deterioration in displayed image quality in the event of occurrence of a dropout in the recorded signal (hereinafter referred to as dropout compensation), etc.
However, in cases where signal processing by the conventional video camera is digitized, it has been necessary to provide an A/D converter at each of signal input parts and a D/A converter on the signal output side. Therefore, even if the details of signal processing are equivalent to those of analog signal processing, the number of component parts is increased by the parts added for the digital signal processing. Further, according to the conventional arrangement, the digital processing circuits are arranged discretely for image pickup system, a recording system and a reproduction system. The use of discrete digital processing circuits greatly increases the scale of circuit arrangement and thus has been disadvantageous in respect to a reduction in cost and size.